of Miscible Liquids by Distillation. 643 



For the first of the experiments just described Table V- 

 shows the volume of benzene collected, the percentage of 

 benzene in the mixture remaining in the apparatus, the 

 volume of distillate collected per minute and the thermal 

 efficiency. The slow rise of temperature and the gradual 

 increase in the rate of distillation and in the thermal 

 efficiency during the first 50 minutes are attributed to the 

 expenditure of heat iu warming the column and the thermo- 

 meter. When a steady state was attained, the thermal 

 efficiency was sensibly constant at 44 per cent., falling 

 slightly as the mixture became poor in benzene. 







Table V. 







Time: 

 ninute?. 



c.c. 

 collected. 



c.c. 

 per 

 mir. 



Mixture 



per cent, of 



benzene. 



Temp. 



°C. 



Thermal 

 efficiency 

 per cent. 







00 





80 



68-8 





10 



1-6 



0-28 . 



79 



79-6 



25 



20 



5-2 



0-39 



78 



79-9 



34 



30 



0-3 



043 



76 



80-1 



38 



40 



138 



0-46 



72 



80-2 



42 



50 



18-5 



0-45 



68 



80-2 



42 



60 



23-0 



045 



63 



80-2 



44 



70 



27-3 



0-43 



56 



80-2 



44 



80 



31-4 



0-38 



46 



802 



43 



90 



34-8 



0-29 



34 



80-2 



39 



100 



37-3 



0-195 



21 



80-2 



38 



110 



38-6 



0085 





80-1 





120 



39-1 



0-035 





80-0 





130 



39-35 



0-02 





79-2 





140 



395 



o-oi 





77 3 





The composition of the mixture given in column 4 is 

 obtained from the original composition by deducting the 

 amount of benzene collected. When the composition falls 

 to 20 per cent, of benzene only 2*5 c.c. of benzene remain, 

 and the calculated percentage ceases to be trustworthy. 



Experiments made with slower rates of heating showed 

 that the greatest thermal efficiency was obtained when distil- 

 lation was at the maximum rate to yield pure benzene. At 

 170 calories per minute the thermal efficiency was 44 per 

 cent., with a heat supply of 146 calories per minute it was 

 35 per cent., and at 128 calories per minute it was only 

 5 per cent. 



